| From: | Steve Singer <steve(at)ssinger(dot)info> |
|---|---|
| To: | Petr Jelinek <petr(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Andres Freund <andres(at)2ndquadrant(dot)com>, Jim Nasby <Jim(dot)Nasby(at)BlueTreble(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Anssi Kääriäinen <anssi(dot)kaariainen(at)thl(dot)fi>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Jaime Casanova <jaime(at)2ndquadrant(dot)com> |
| Subject: | Re: tracking commit timestamps |
| Date: | 2014-11-09 16:57:53 |
| Message-ID: | BLU436-SMTP244603CD8EA872FCA539042DC830@phx.gbl |
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| Lists: | pgsql-hackers pgsql-www |
On 11/07/2014 07:07 PM, Petr Jelinek wrote:
> The list of what is useful might be long, but we can't have everything
> there as there are space constraints, and LSN is another 8 bytes and I
> still want to have some bytes for storing the "origin" or whatever you
> want to call it there, as that's the one I personally have biggest
> use-case for.
> So this would be ~24bytes per txid already, hmm I wonder if we can
> pull some tricks to lower that a bit.
>
The reason why Jim and myself are asking for the LSN and not just the
timestamp is that I want to be able to order the transactions. Jim
pointed out earlier in the thread that just ordering on timestamp allows
for multiple transactions with the same timestamp.
Maybe we don't need the entire LSN to solve that. If you already have
the commit timestamp maybe you only need another byte or two of
granularity to order transactions that are within the same microsecond.
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